For many years the electronics or semi-conductor industry has been using various types of ovens and furnaces for high volume heating and/or cooling applications. In the oven and furnace industry many inventions have occurred. However, most of them have been directed to innovations in either cooling or heating of the parts that are being processed.
U.S. Pat. No. 4,554,437 (Wagner et al.) discloses a continuous speed belt type tunnel oven which allows a user to select different top and bottom temperatures within each of the plural cooking zones.
U.S. Pat. No. 4,693,211 (Ogami et al.) discloses a surface treatment apparatus, which is composed of a supporting die for holding a substrate thereon to heat and/or cool the substrate. A cover defines a treatment space over the entire surface of the substrate on the supporting die. Preferably, a heat-insulating housing could be outside the cover.
U.S. Pat. No. 4,886,954 (Yu et al.) discloses a hot wall diffusion furnace and a method for operating the furnace. Yu et al. disclose that the heating elements in the upper section of the furnace be connected to one circuit, and the heating elements of the lower section of the furnace be connected to a second circuit, and that each circuit be controlled in response to the temperature in that section, so that uniform temperature can be obtained in the processing chamber.
U.S. Pat. No. 4,903,754 (Hirscher) discloses a method and apparatus for the transmission heat to or from plate like object. The plate-like object, such as a Si wafer, is held on a back plate and inside a cover. This patent discloses both the heating and cooling of the plate-like object.
U.S. Pat. No. 4,950,870 (Mitsuhashi et al.) discloses a heat-treating apparatus having at least three heaters and the power to these heaters can be supplied from independent power sources so that the heating temperatures of the individual heaters can be freely adjusted. Additionally, the multiple heaters in the vertical furnace attain a uniform heat distribution throughout the heating zone.
U.S. Pat. No. 4,966,547 (Okuyama et al.) discloses a heat treatment method using a zoned tunnel furnace. The furnace has roller conveyer and each of the zones in the furnace walls are provided with electric resistance heating wires. The heaters in each zone are under programmed control, independent of the heaters in the other zones. Similarly, the roller conveyer in each zone can be driven independent of the roller conveyer in the other zones by programmable controllers.
U.S. Pat. No. 4,982,347 (Rackerby et al.) discloses a process and apparatus for producing temperature profiles in a workpiece as it passes through a belt furnace. Each of the heaters has their own separate thermostats, which enables the temperature of each heater to be separately set. Thus a workpiece can be subjected to a temperature profile which varies from heater to heater along the passageway.
U.S. Pat. No. 5,054,418 (Thompson et al.) discloses a device for holding wafers of semi-conducting materials during thermal processing or coating, where the device is a cage boat having removable slats.
The parts or products using conventional furnaces and ovens have changed over time. Some of the parts have been getting larger and others are getting smaller, and still other require more stringent processing controls. Therefore, it has become increasingly difficult to do the same type of processing on the parts, as done by the ovens and furnaces known in the art.
For some parts the thermal mass or thermal weight resists being heated quickly, and therefore they may have to be processed for a longer period. Another factor is that newer and different materials are being used to make these parts, and these newer materials require different heating regimes. These issues are further compounded by the fact that now closer temperature control and lower intra-part gradients are being required by the electronics industry.
The manufacturers of conventional ovens and furnaces have made quite a few upgrades to their system in response to the industrial needs. Some upgrades include providing better and more efficient gas flows. Others have provided improved zone separation. And, still others are providing better cooling in the cool down section. Most of these changes are required because the parts or products are less tolerant to thermal process irregularities and the resultant mechanical stresses, etc.
Another problem faced in the use of conventional ovens or furnaces is that when flux or similar contaminants are used in a conventional oven or furnace they get deposited on the walls of the furnace creating a contamination problem for the furnace as well as the parts that are being processed in the furnace. Flux and similar contaminants results from many processes, such as a soldering process, and therefore cannot be eliminated. Similarly, there are other solvents which evaporate from the surface of the part, as the part is being heated, and they enter the flow of the gases in the furnace, flowing from the hotter end or area to a colder area. This causes the vaporized solvents and similar other material to condense on cooler furnace areas or parts and this collects as contamination.
For an application, such as chip join, the operation is characterized by loading many parts on a belt, followed by continuous movement of the belt through the furnace's heating and/or cooling areas, and thus it is not very practical to stop and clean the furnace for a different part and/or a different process.
Therefore, during a typical high volume heating and/or cooling applications care must be taken to prevent the parts being processed from being contaminated with contaminants that are inside the furnace, and that the contamination be kept to the minimum.
For the above-mentioned reasons, parts cannot always be processed within specification using the conventional ovens or furnaces, and therefore there is a need for improvement in the furnace and oven industry.
The above-mentioned and other problems have been overcome by the novel apparatus and the process of this invention.